叠层有机太阳电池中载流子在连接层复合机理的研究

The tandem structure can overcome the two major limitations of narrow absorption spectra and thermerlization losses in single-junction devices, which provides an effective approach to boost the efficiency of organic solar cells. It is calculated that the efficiency of organic tandem solar cells can be enhanced from the sate-of-the-art 11% of the single-junction devices to the level of 15%. Although the efficiency of organic tandem cells has progressed rapidly in recent years, a systematic understanding of the charge recombination mechanism is still missing. This proposal focuses on the synthesis of aluminum doped zinc oxide (ZnO:Al) with different doping concentrations. In order to obtain qualified ZnO:Al nanoparticles that can be used as electron transport layer in organic solar cells, the crystal structure, morphology of the nanoparticles and the electronic properties of the films are controlled by adjusting the reaction conditions. Using the obtained ZnO:Al as N-type electron transporting material in combination with the classic P-type hole-transporting material PEDOT:PSS as the prototype of charge recombination center, key factors such as the optoelectronic properties of the materials, band structures and contact properties of the interfaces that may affect the efficiency of charge recombination can be investigated. Simultaneously, using transparent and conducting silver nanowire film as an intermediate electrode, three-terminal series-connected tandem devices can be manufactured which allows to study the relationship between the performance of the tandem cell and the two sub-cells. This work would provide important tutorial information on the fabrication of high-efficiency organic, inorganic and hybrid tandem solar cells.

叠层电池结构能有效克服单节太阳电池窄吸收和高能量光子热损耗两大缺点，理论上能将有机太阳电池的光电转换效率从当前的11%提升到15%。虽然叠层有机太阳电池的效率在近些年取得显著的提升，但对光生载流子在连接层（又称复合中心）的复合机制仍缺乏系统的研究。本项目将首先专注于不同浓度的Al掺杂ZnO（ZnO:Al）纳米颗粒的合成，研究反应条件和掺杂水平对颗粒的晶体结构、形貌和薄膜的光电性能的影响，开发出可用于有机太阳电池的N型电子传输材料。进而，结合经典P型空穴传输材料PEDOT:PSS构筑载流子复合中心，研究材料的光电属性、界面的能级结构和电学接触等特性对载流子复合效率的影响。同时，使用透明导电银纳米线作为中间电极开发三电极结构串联电池，探索叠层电池的光电性能与子电池性能之间的关系。本项目的实施将为高效率叠层太阳电池（包括有机、无机和杂化太阳电池）的开发提供重要的参考信息。

项目围绕叠层太阳能电池载流子隧穿结的界面层材料设计与制备展开，使用聚苯乙烯磺酸钠对P型空穴传输材料PEDOT:PSS进行掺杂，调节功函数和空穴迁移率，实现有机和钙钛矿太阳能电池开路电压的调节，同时发现交联的PEDOT:SS具有优良的抗溶剂侵蚀性能。使用纳米银线作为中间透明电极组装三电极叠层电池，揭示了隧穿结的非欧姆接触是叠层电池填充因子和短路电流损失的主要原因。将掺杂的空穴传输材料应用到铅锡混合钙钛矿电池中，结合构筑2D/3D层状异质结对活性层表面进行钝化，能显著降低界面的非辐射复合，将窄带隙钙钛矿电池（Eg=1.33 eV）的开路电压从0.71 V提升到了0.78 V，转换效率达到15.15%。最后，通过设计具有阶梯能级排列的PEDOT:PSS/PTAA双空穴传输层，抑制载流子在界面处的复合，结合路易斯碱对晶体形貌的调控，在相对粗糙的柔性衬底上制备了致密均匀的钙钛矿薄膜，制备的柔性太阳能电池效率和填充因子分别达到19.41%和81%。基于表界面能级调控以及隧穿结的电学性能调节策略为下一步高效率柔性叠层电池和组件开发提供了可参考的研究思路。